NERSC Initiative for Scientific Exploration (NISE) 2010 Awards

ITER rapid shut-down simulation

Valerie Izzo, General Atomics

Associated NERSC Project: Disruption and disruption mitigation simulations (m455), Principal Investigator: Valerie Izzo

This research will help develop scenarios to quickly shut down fusion reactor plasmas in case of unexpected occurrences that may damage machine components.

Research on safe rapid termination of tokamak discharges is primarily targeted toward implementation on ITER; however, simulation of ITER is considerably more challenging that smaller tokamaks. Rapid termination simulations of the DIII-D and C-Mod tokamaks have been carried out through the entire current quench phase with NIMROD (a time scale of 1-5 ms). These simulations include the interaction between impurity radiation and MHD, and a fast electron orbit model for understanding runaway electron confinement. These tools can be applied directly to ITER given sufficient computational resources.

Previous NIMROD simulations of an ITER rapid shutdown have been limited to simplified scenarios and only the early current quench phase. The entire current quench on ITER will last 10s of ms, while the spatial scale is 3 times larger in linear dimension than DIII-D. With similar toroidal resolution, 9 times more grid points in the poloidal plane, and several times longer simulations time, a complete ITER rapid termination scenario will consume about 1,000,000 cpu hours on franklin using several thousand processors, compared with a DIII-D simulation consuming 20,000 hours on roughly 1000 processors.

From the ITER rapid shutdown simulation we will better understand the MHD fluctuation spectrum of an ITER plasma cooled by high-Z impurities, evolution of the electric field, confinement time of high energy runaway electrons, and strike points of escaping runaway electrons. Some of these characteristics may differ greatly from DIII-D and C-Mod.